Intraspecific Host Preferences of Mopane Moths (Imbrasia belina) in Mopane (Colophospermum mopane) Woodland

Abstract

Colophospermum mopane trees are a common larval food plant of the mopane moth (Imbrasia belina), which commonly reaches outbreak proportions. Our study investigated factors determining host tree choice by ovipositing mopane moths within a single host species (C. mopane). Tree size was the primary determinant of oviposition at both the habitat (tall riverine-, medium height woodland-and short-shrub mopane) and individual tree scale, with an increase in the number of egg masses with increasing tree size (estimated by height and canopy volume). Preference for larger trees was only evident at the habitat scale, however, as individual trees were utilized as expected according to the availability of their canopy size class. More detailed tree characteristics, such as leaf size, shoot size, stem number and even leaf chemistry (protein:tannin ratio and total polyphenols) had no influence on host choice. Host choice was based on the most obvious measure of resource abundance, namely tree size, as expected for an outbreak species, since resource availability rather than nutritional quality is likely to be the primary determinant of larval survival.

Differential effects of defoliation by mopane caterpillars and pruning by African elephants on the regrowth of Colophospermum mopane foliage

“…Here, the decrease in leaf and shoot size was accompanied by a simultaneous decline in chemical defences. Furthermore, while the effect of natural pruning by elephant was similar to simulated pruning in this study, Hrabar (2005) found a negative impact on both regrowth (no increase in leaf size such as this study) and chemical defences (decreased tannin:protein ratio) from elephant browsing of mopane trees in the Kruger National Park. This shows that even when stored resources appear to be limited, the reduced investments in growth and chemical defence still do not take place at the expense of each other.…”

“…Foliar chemical composition was only found to change after natural caterpillar defoliation, with reduced chemical defence in the regrowth. These lower chemical defences are unlikely to be due to caterpillars avoiding trees with high chemical defences, as Hrabar (2005) found host leaf chemistry had no influence on host choice by ovipositing female moths.…”

“…In February 2004 the trees in each treatment were revisited and the following variables were measured: leaf size, shoot length, shoot density and foliar chemical composition. Leaf length was used as an indicator of leaf size (as leaf length and width are correlated; Hrabar 2005), measured (in mm) from the growth point to the tip of the right leaflet. Fifteen mature undamaged leaves were measured for each tree and were chosen randomly from all sides of the canopy, between a height of 0.5–2 m. The length of the current year's growth (which was clearly identifiable) was measured for 15 shoots per tree, to the nearest cm.…”

“…In March 2004, once the regrowth on the naturally defoliated trees had stopped growing (see Hrabar 2005), all browsed (elephant and caterpillar) and partnering non-browsed trees were revisited and information on the current year's growth recorded. Leaf size, shoot length and shoot density were measured as described above.…”

The Occurrence and Characteristics of Imbrasia belina (Westwood, 1849) in the Subtropical Region of KwaZulu-Natal Province, South Africa

“…It avoided the small S. birrea trees less than 3 m in height. This might be taken as evidence that the females exercise selection of host plant at the individual tree scale (Hrabar et al 2009). The avoidance of small trees (under 3 m), in the present study could be a strategy to ensure adequate forage for the larvae, as it would run out before the pupation stage on small trees.…”